U.S. patent number 4,424,496 [Application Number 06/310,011] was granted by the patent office on 1984-01-03 for divider/combiner amplifier.
This patent grant is currently assigned to Raytheon Company. Invention is credited to George H. MacMaster, Lawrence J. Nichols.
United States Patent |
4,424,496 |
Nichols , et al. |
January 3, 1984 |
Divider/combiner amplifier
Abstract
A divider/combiner amplifier circuit divides input power through
a sectored coaxial line to a plurality of longitudinal parallel
channels spaced around the circumference of a cylinder; the power
in each channel is amplified by a semiconductor device; and the
amplified power is combined in another sectored coaxial line. A
microwave waveguide connected to the input and output of each
amplifying device confines the microwave energy of the operating
mode to the longitudinal channel formed by said waveguide. Each
waveguide extends longitudinally along the cylinder and each is
circumferentially spaced from its neighboring waveguide by a space
which forms a cut-off waveguide to the operating mode. In the event
of a failure of one or more amplifying elements, the space allows
the failure mode to propagate radially to microwave absorbing
material where it is absorbed to prevent reflection back into the
longitudinal waveguide and thus effectively isolates the failure to
provide a gradual deterioration of the amplifier circuit
performance with element failure.
Inventors: |
Nichols; Lawrence J.
(Burlington, MA), MacMaster; George H. (Lexington, MA) |
Assignee: |
Raytheon Company (Lexington,
MA)
|
Family
ID: |
23200611 |
Appl.
No.: |
06/310,011 |
Filed: |
October 13, 1981 |
Current U.S.
Class: |
330/286;
330/56 |
Current CPC
Class: |
H03F
3/58 (20130101) |
Current International
Class: |
H03F
3/54 (20060101); H03F 3/58 (20060101); H03F
003/60 () |
Field of
Search: |
;330/54,56,286,287 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
4234854 |
November 1980 |
Schellenberg et al. |
4283685 |
August 1981 |
MacMaster et al. |
|
Primary Examiner: Mullins; James B.
Assistant Examiner: Wan; Gene
Attorney, Agent or Firm: Santa; Martin M. Pannone; Joseph D.
Sharkanksy; Richard M.
Claims
What is claimed is:
1. A microwave amplifier comprising:
a first waveguide means;
an amplifying means connected to said first waveguide means to form
a waveguide amplifier having an input and an output;
a plurality of said waveguide amplifiers having their inputs and
outputs connected in parallel;
means adjacent said first waveguide providing a second waveguide
between each pair of adjacent first waveguides of said waveguide
amplifiers which prevents the operating mode of each of said
waveguide amplifiers from propagating through said second waveguide
means;
a microwave absorber terminating each second waveguide; and
said absorber absorbing the microwave energy transmitted through
said second waveguide from said first waveguide means.
2. The amplifier of claim 1 wherein:
said first waveguide means comprises first and second conductors
separated in a first direction by a first mirowave propagation
space;
said first and second conductors of each of said adjacent waveguide
amplifiers being spaced from each other, respectively, in a second
direction transverse to said first direction to form said second
waveguide means, said second waveguide means formed by adjacent
said first conductors and formed by adjacent said second conductors
providing isolation between said first waveguide means and said
absorber and acting as a reactive attenuating waveguide beyond
cutoff to the operating mode of said first waveguide means and as a
transmissive waveguide between said absorber and said first
waveguide means of other modes of said first waveguide means.
3. The amplifier of claim 1 comprising in addition:
an input means;
an output means;
means for equally dividing microwave power applied to said input
means between said waveguide amplifiers; and
means for combining the output power of each of said waveguide
amplifiers and providing said combined power to said output
means.
4. The amplifier of claim 3 wherein said means for dividing the
input microwave power and combining the output power each comprises
a radially stepped impedance transforming coaxial line having spced
inner and outer coaxial conductors; and
said inner and outer conductors having a plurality of slots in the
direction of the length of said coaxial line, said inner and outer
conductor slots being in radial alignment, said spaced slotted
inner and outer conductors being a part of said first waveguide
means.
5. The amplifier of claim 4 comprising:
said amplifying means comprising a microwave transmission line
comprising first and second radially spaced conductors having the
same width as the greatest width of said slotted inner and outer
coaxial conductors, respectively;
said first and second radially spaced conductors being adapted to
be attached at each end to the inner and outer conductors,
respectively, of said input dividing means and said output
combining means;
a plurality of amplifying elements; and
said first conductor being interrupted and adapted to be serially
connected at said interruption to the input and output terminals of
said amplifying means.
6. A microwave amplifier comprising:
a plurality of parallel first microwave waveguides, each first
waveguide comprising a pair of conductors separated by a microwave
propagation space;
a plurality of microwave amplifier elements;
each first waveguide having an input end and an output end and
having one of said amplifier elements connected thereto to amplify
microwave energy applied to the output end of the first
waveguide;
each of said first waveguides being connected in parallel so that a
signal applied to the input end of said parallel connection is
amplified in each first waveguide and combined at the output
connection of said first waveguides;
each conductor of a pair of conductors spaced to form said first
waveguide being laterally spaced from the corresponding conductor
of an adjacent first waveguide to provide slots extending along and
between said adjacent conductors;
corresponding spaced adjacent conductors forming second and third
waveguides, said second and third waveguides each being a
reactively attenuating cutoff waveguide to the operating mode and
frequency at which amplification takes place in the first
waveguide;
said second and third waveguides having microwave absorbers
disposed at the slot ends most remote from said microwave
propagation space of said first waveguide, said absorbers acting as
a termination for said second and third waveguides for microwave
energy propagating in said second and third waveguides.
7. The microwave amplifier of claim 6 wherein each of said
conductors of said pair of conductors forming each of said first
waveguides has a thickness in the direction transverse to said
microwave propagation space of said first waveguide, said thickness
being sufficient to cause said conductors to provide said second
and third waveguides in said thickness direction.
8. A divider/combiner amplifier circuit comprising:
a cylindrical array of a plurality of microwave transmission lines
extending longitudinally along the surface of said cylindrical
array and circumferentially spaced from each other along said
surfaces;
each of said transmission lines comprising a pair of longitudinally
extending radially spaced inner and outer electrical
conductors;
a plurality of amplifier elements, each connected to one of said
transmission lines to amplify microwave energy entering one end of
said transmission line and exiting at the other end of said
transmission line;
a first and second coaxial line each having inner and outer
concentric conductors;
each said coaxial line at one end having a larger diameter of both
inner and outer conductors than at the other end, said larger
diameter conductors being connected to the ends of said
transmission line and being longitudinally slotted to correspond to
the circumferential spacing and width of the conductors of said
transmission lines;
the other end of said coaxial line being of smaller diameter and
unslotted;
microwave absorbers at the radial ends of the circumferential
spaces between the inner and outer conductors of said transmission
line and said larger diameter coaxial line; and
said circumferential spaces and the radial thickness of said
conductor and said larger diameter coaxial line providing
waveguides beyond cutoff for attenuating the operating mode of the
transmission lines and a propagation space for modes other than the
operating mode to cause said microwave absorbers to resistively
terminate said waveguide beyond cutoff.
9. The amplifier of claim 8 comprising:
each said coaxial line having a plurality of inner and outer
concentric coaxial conductor diameters intermediate those at its
ends to provide a stepped coaxial transmission line.
10. The amplifier of claim 9 wherein one of said microwave
absorbers comprises a hollow cylindrical absorber whose inner
radius is greater than and which surrounds the spaced outer
conductors of the array of the plurality of spaced microwave
transmission lines and said slotted coaxial lines; and
the other of said microwave absorber comprises a stepped
cylindrical absorber whose diameter is less than that of and which
is surrounded by the spaced inner conductors of the array of the
plurality of spaced microwave transmission lines and said slotted
coaxial lines.
11. The amplifier of claim 10 wherein said microwave absorbers have
a resistivity which is less in the immediate vicinity of said slots
than at farther removed positions within the absorber to provide a
tapered resistor having small reflections of microwve energy
incident upon it through said slots.
12. A microwave amplifier comprising:
means for amplifying microwave energy comprising a radially spaced
pair of conductors forming a microwave transmission line in the
region between said conductors;
means for providing an amplifier element within said transmission
line for amplifying microwave energy passing down said line;
a plurality of said transmission lines and corresponding amplifier
elements extending longitudinally and spaced from each other along
the circumference of a cylinder to form slots spaced along said
circumference which extend longitudinally;
a microwave energy absorber at each radial end of said slots;
and
said pair of transmission line conductors, each extending radially
a sufficient distance and spaced sufficiently closely to form a
radially directed transmission line which is beyond cutoff at the
operating mode frequency and which allows transmission to said
absorbers for modes other than the operating mode.
Description
BACKGROUND OF THE INVENTION
This invention relates to solid state microwave amplifiers and more
particularly to divider/combiner circuits for obtaining higher
power output than can be obtained from one solid state amplifier by
appropriately combining the output power from more than one
amplifier. More particularly, the circumferential divider/combiner
circuit of the invention combines the output power of a moderate
number of high frequency bipolar and/or field effect transistors to
provide high power amplification in the 8-20 GHz frequency band. In
this frequency range, power amplification techniques are almost
totaly dominated by thermionic-cathode microwave tubes with some
limited applications for one-port negative resistance semiconductor
devices. The need for higher-power solid state microwave amplifiers
exists in order to provide amplifiers of smaller size, lighter
weight, increased reliability and lower cost than are presently
available.
In the prior art, the semiconductor devices which are available for
amplification in the 10 GHz frequency range are limited in the
output power that they can provide. Thus, although they have a
broad bandwidth and have the advantage of not utilizing thermionic
cathodes, their lack of ability to produce high power is a
substantial limitation to their application. These active
semiconductor devices have been incorporated into prior art
circuits to increase their output power by paralleling a number of
devices. However, it has been found that paralelling of individual
semiconductor devices has disadvantages in reduction of efficiency
and the effect of paralleling upon the impedance at the input and
the output of the paralleled devices which limits the number of
such devices which may be paralleled.
When using more than one amplifier because the required output
exceeds the capability of a single device, such as a high frequency
transistor, several amplifiers can be connected in parallel. There
are disadvantages and dangers in the simple parallel connection. An
input VSWR of 1.22, for example, represents a reflection power loss
of only 1%. But if two devices both having a VSWR of 1.22 are
connected in parallel, the power split between them depends on the
impedance ratio which in this case could be as high as 1.5 if the
phases of the two reflections were 180.degree. apart. Similar
arguments can be made about output impedances. Not only is the
power divided unequally, but if one unit fails because of unequal
power split or for other reasons, the resulting high VSWR can
adversely affect the remaining units.
A problem arises in prior art divider/combiner circuits that
utilize integral damping resistors to provide isolation between
paralleled solid state amplifiers. These integral damping resistors
introduce instability and also reduce efficiency in the operating
mode. Although, in the prior art divider/combiner circuits the
isolation resistors are connected so that currents should not flow
in the operating mode, the distributed reactances within the
circuit do produce current flow in the isolation resistors in the
operating mode; and, hence, the stability and efficiency of the
divider/combiner circuit is reduced.
Although solid state power amplifiers using combined negative
resistance diodes are becoming available for use in the 8-20 GHz
frequency range, they have inherent problems with noise
performance, limited dynamic range, and poor stability which limits
their utility. Transistors are presently being developed which
operate in this frequency range and have demonstrated 5 watts
output with 5 db gain at 8 GHz and 1/2 watt output with 5 db gain
at 20 GHz. Numerous applications are envisioned for solid state
microwave amplifiers delivering 10-50 watts output power. Assuming
90 percent combining efficiency can be achieved, a reasonable
number of existing transistors do provide the desired output power
when combined as in this invention.
SUMMARY OF THE INVENTION
The aforementioned problems are overcome and other advantages are
provided by this invention of a circumferential divider/combiner
circuit in which the field patterns and electrode geometry are such
that no fields of the operating mode reach the isolation resistors.
The isolation resistors are effectively out of the circuit unless
there is a mismatch at one or more of the amplifier ports at which
occasion the resistors are coupled by the resulting fields and
thereby prevent the buildup of high Q resonance which could damage
the active elements. The isolation resistors are tapered in order
to reduce reflection of the energy of the mismatch produced mode by
providing a matched load.
The divider/combiner amplifier circuit combines the output power of
more than one solid state amplifying device spaced around the
circumference of a cylinder. The cylinder has an input port which
through a sectored coaxial line divides the incoming energy which
is to be amplified into parallel channels, amplifies each channel
with a conventional transistor of either the FET or bipolar type,
and after amplification combines through a sectored coaxial line
the output powers from each transistor which is provided at the
output port. The circumferentially spaced channels are formed of
longitudinally slotted concentric inner and outer electrically
conducting cylinders. Each channel acts as a microwave waveguide
which is connected to the input and output of each amplifying
device and confines the microwave energy of the operating mode to
the longitudinal channel formed by said waveguide. The inner and
outer conductors of the waveguide extend radially and also
longitudinally along the cylinder and each conductor is
circumferentially spaced from its neighboring wall by a space to
also form a waveguide in the radial direction which is below
cut-off to the operating mode. In the event of a failure of one or
more amplifying elements the radial waveguide allows a failure mode
to propagate inwardly and outwardly radially to microwave absorbing
material (isolating resistors) where it is absorbed to prevent
reflection back into the longitudinal channel and thus effectively
isolates the failure to provide a gradual deterioration of the
amplifier circuit performance with element failure. The structure
also provides the sectored coaxial line impedance matching circuits
at the ends of the channels to couple the input power from the
input port to the inputs of the channels and to couple the power
from the outputs of the channels to the output port.
It is an object of this invention to provide a multiple device
structure which can be used to obtain higher output power than for
single devices, to provide graceful degradation of system operation
with failure of the devices, and to extend the system life by
operating each device conservatively. It is a more specific object
of this invention to combine the power output of transistors to
obtain a higher output power as an alternative to power amplifier
tubes typically in the frequency range mentioned above. It is a
further object of the invention to provide a structure of small
size and weight, and with low production costs. It is a further
object of the invention to provide a structure which can be
operated with existing high frequency transistors of limited power
output. It is a further object of the invention that the structure
be a low loss circuit capable of operating in the frequency band of
8-20 GHz with at least 20% bandwidth and having high isolation
between the input and output ports.
These and other objects will be apparent from the following
description of the invention when considered in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The aforementioned objects and features of the invention are
explained in the following description taken in conjunction with
the accompanying drawings:
FIG. 1 is a perspective view partially in a cross-section of the
structure of the invention showing the multiple channels;
FIG. 2 is a graphical cross-sectional view of the invention with an
exploded view portion;
FIG. 3 shows the transistor and transistor mount for each channel
of the structure of the invention.
FIG. 4 shows a partial cross-sectional view at section 4--4 of FIG.
1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The circumferential divider/combiner circuit 10 of this invention
is a new power combining scheme for transistor amplifiers which
overcomes the problems associated with insertion loss, bandwidth,
and isolation properties that are inherent in other types of power
combiner approaches. A key feature of the circumferential
divider/combiner approach is the geometrical configuration of the
coaxial transformers 241, 242 which are formed by copper steps 240
to keep line losses low and for wide bandwidth. This
circumferential design along with the external damping resistors 14
also ensures that there are no overload problems or stability
problems of this multiamplifier network that do not already exist
for an individual amplifier.
In addition to solving the electrical problems, the power combining
approach of this invention provides a superior configuration for
cooling transistor amplifiers. For divider/combiner circuits, the
power limits are usually set by the ability to control device
temperature.
A ten-channel version of the circumferential divider/combiner
circuit 10 is shown in the figures. This circuit 10 may be
considered as a split 4-step coaxial transformer 241 in the divider
circuit followed by a split 4-step coaxial transformer 242 in the
combiner circuit. Inner 26 and outer 24 coaxial cylindrical
conductors are split into ten sections to provide proper mode and
isolation characteristics. The central regions 243, 244 which are
divided into ten 50 ohm parallel plane transmission lines 12 are
spaced, and 50 ohm amplifiers 17 are inserted in the spaced region.
As shown schematically in FIG. 2, the amplifiers 17 are mounted on
the outer conductor of the transmission line 33 face inward,
providing a superior configuration for cooling. The length of this
copper heat sink (transmission line 33) accommodates the matching
networks 34, 43 and transistor amplifiers 17. The heat sink 33 on
which the transistor amplifier 17 is mounted can be removed by
screws 20, 21 and different power amplifiers may be mounted for
replacement of defective amplifiers as desired. In addition to
transistor amplifiers, transistor devices and impatt diodes may be
mounted on the heat sink 33 and connected to the circumferential
divider/combiner circuit 10.
The high power handling capabilities of the circumferential
divider/combiner circuit 10 should also be noted, along with the
electrical features of wide bandwidth, low loss, and high
isolation. There are no individual isolation resistors; isolation
is achieved by means of inner 32 and outer 14 coaxial loads which
can handle very high powers. These loads are effectively out of the
circuit unless there is a mismatch at one or more of the transistor
ports.
Although a ten-channel version of the circumferential
divider/combiner was built and tested, a large number of channels
(N) may readily be incorporated. The input coax is split up into N
sections. There is continuity of center and outer conductors. If
each amplifier operates at an impedance level equal to the coax
impedance, the parallel combination represents an impedance
mismatch of N to 1. Thus, there is the necessity for the wideband
stepped or tapered matching section.
Since the entire structure is symmetrical about the axis 27, it is
convenient to use (instead of individual amplifier connections as
terminals) a set of symmetry terminals, each mode consisting of a
symmetric distribution of voltages around the ring. In such a
system the scattering matrix of the circumferential divider is
obtained by a matrix transformation which indicates that any
symmetric wave pattern excited on the divider (except the desired
one) should be absorbed by non-reflecting damping resistors
(transmission is impossible by symmetry). If such matched
terminations are achieved, the divider performance will be
ideal.
The matched terminations provided by resistors 14, 32 imply some
sort of stepping or tapering of the resistors. The termination
configuration looks like FIG. 2 with resistors inside 32 or outside
14 or both. If resistors are on one side of channels 12 only, the
other side can be connected together without the slots 13, 28 to
form a "ground" plane. The "ground" plane version of the invention
is not shown in the figures since that embodiment is apparent from
the preferred embodiment which is considered to provide better
performance.
Referring now to FIGS. 1-4 there is shown an amplifier assembly 10
which, in accordance with the invention, comprises a cylindrical
structure 11 which contains a plurality of channels 12 for the
amplification of the microwave energy. The channels 12 are
separated by air gap slots 13 which confine the electromagnetic
energy in each channel 12. The outer portion of the channels 12 and
the slots 13 are enclosed with a hollow cylinder of microwave
energy absorbing material 14, typically a carbon-loaded epoxy. The
input terminal 15 of the amplifier assembly 10 is at one end of the
cylinder 11 while the output terminal 16 is at the other end of
assembly 10. Also shown in FIG. 1 are the amplifier subassemblies
17 with terminals 18 and 19 through which power is provided to the
amplifier element of the amplifier subassembly 17. The amplifier
subassemblies 17 are fastened into their respective channels 12 by
pressure contact produced by screws 20, 21. Conventional electrical
connectors (not shown) connected to a power source provide the
appropriate power to terminals 18, 19 of the transistor 46 of
amplifier subassembly 17. The cylindrical absorber 14 is assembled
from two semi-cylinders 14', 14" abutting along line 142 and having
holes 141 sufficiently large to clear the leads 18 and 19 when
being placed over the amplifier assemblies 17 and cylinder 11.
Typically, there may be ten amplifier assemblies 17 uniformly
distributed around the circumference of the cylinder 11.
Referring now to FIG. 2 there is shown in isometric view of the
amplifier circuit 10, partially in cross-section and partially in
exploded view. The microwave input connector 15 is attached to a
cylindrical block 22' which is attached to the cylindrical
structure 24' by screws 23. Cylindrical structure 24' has radial
slots 13 which extend longitudinally in the direction of axis 27.
The slots 13 in the cylindrical structure 24' begin a short
distance 29 from the interface 221 of the cylinders 22, 24 and
isolate the channels 12. The cylinder 24' is electrically connected
through cylindrical block 22' to the outer conductor of the
connector 15. The inner conductor 25 of connector 15 extends
longitudinally inwardly toward the center of the amplifier assembly
10 where it makes electrical contact with a stepped cylindrical
electrical conductor 26' coaxial with the axis 27 of the amplifier
assembly 10. The interior stepped conductor 26' has slots 28 which
correspond to and are radially aligned with the slots 13 of the
stepped outer conductor 24. The portions of the inner and outer
stepped conductors 24', 26' between their respective slots 13, 28
comprise a stepped coaxial waveguide for the confinement in space
36' of the electromagnetic energy which enters at connector 15. The
locations 29, 31 of the beginning of the slots 13, 28,
respectively, determine where in the stepped coaxial line 36' the
input microwave energy starts being divided into separate channels
12. Slots 28 of the interior stepped cylindrical conductor 26 begin
at a location 31 closer to the longitudinal center of the assembly
10 than do the slots 13 and extend radially toward the centered
axis 27 of the assembly 10. Beginning slots 28 and 13 at different
axial locations provides a gradual transition from the unslotted
coaxial line 25 near the interface 221' to the channels 12 and
thereby reduces impedance mismatch in this transition region. The
radii and longitudinal lengths of the steps of the stepped
conductors 24, 26 are chosen to provide a broad band impedance
match between the impedance of the coaxial line 25 at the input and
output terminals 15, 16 of the input and output lines 37, 38
connected to the emitter and base, respectively, of the transistor
amplifier element 46. The base of transistor 46 being connected to
conductor 33.
Located in the interior of the stepped conductors 26', 26" and
extending longitudinally between the conductors 26', 26" is a
matching stepped cylindrical microwave absorber 32, typically
carbon-loaded epoxy, which absorbs microwave energy which leaks
through the slots 28 of the stepped inner conductor 26.
The outer stepped conductors 24 are attached to the end blocks 22
by means of fastener screws 23. The input end 24' and the output
end 24" of outer stepped conductors 24 are connected to input and
output connectors 15, 16, respectively, as illustrated in the
amplifier assembly 10 shown in FIG. 2. The amplifier subassemblies
17 are fastened by screws 20, 21 to the inner and outer stepped
conductors 26, 24, respectively, the assembly forming the channels
12.
Amplifier subassembly 17 is seen in FIGS. 2, 3 to comprise an outer
conductor 33 which is in electrical contact with stepped conductor
24. Subassembly 17 also has inner conductors 34', 34" to which the
input and output terminals, respectively, of transistor 46 are in
electrical contact. Conductors 33, 34 are of the same width as the
channel 12 conductors 24, 26, respectively. Because of the symmetry
of the amplifier assembly 10 the combiner portion of the assembly
10 connected to output terminal 16 is substantially identical to
the divider portion of assembly 10 which is connected to the input
terminal 15.
The bottom portion of FIG. 2 shows the completed amplifier assembly
10 in cross-sectional view, the incoming electrical signal at
electrical connector 15 passes into the impedance-matching stepped
coaxial waveguide region 36' where the signal is divided between
channels 12 formed by the slots 13, 28 between conductors 24', 26',
respectively. The signal in each channel 12 is transmitted along
the channel space 361 between channels 12 and the ceramic 43'
bonded to the inner and outer conductors 34, 33. A cross-sectional
view at section lines 4--4 of the divider/combiner 10 is shown in
FIG. 4 where the electric field lines 50 of the operating mode
(TEM) are shown as concentrated in the space 361 between radially
separated inner and outer conductors 24, 26 of each channel 12. The
radial spaces 13, 28 between conductors 24, 26, respectively, form
the waveguides below cutoff which isolate the operating mode field
from the absorbers 14, 32, respectively. At least 30 db isolation
is desired and the width and radial extent of the spaces 13, 28 are
chosen to provide at least that amount of isolation by the reactive
attenuation of the cut-off waveguide. The conductors 24 also serve
the purpose of thermal conductors of heat produced by the
transistor 46 to the end masses 22', 22" where the heat is
dissipated. The modes, produced when a transistor fails, propagate
through the spaces 13, 28 and are dissipated in absorbers 14, 32,
respectively. The microwave energy enters enters the input terminal
of a commercially available high-frequency FET transistor 46 which
comprises a microstrip line 37 formed on a metallic 35. The
microwave energy is amplified in transistor 46 whose output is
provided on microstrip line 38 where it is propagated into the
ceramic separator 43" from which the amplified signal passes
through the channel spaces 36" of the stepped coaxial line
conductors 24", 26" to the coaxial region in the vicinity of
boundary 221" where the output signal from each of the transistors
is combined before exiting at the output connector 16.
A plan view of the amplifier subassembly 17 is shown in FIG. 3
which illustrates in more detail its construction for confinement
of the high frequency energy to the regions desired and for
minimizing impedance mismatch. Conductor 33 of subassembly 17 has a
constant width and forms a continuation of the outermost portion of
a channel 12. The inner conductor 34 which is of constant width
near its end 340 tapers inwardly to the center line 41 of the
subassembly 17. Typically, the tapered section 341 tapers from 0.3
inches to a width of 0.1 inches which is still substantially wider
than the input microstrip line 37 of the transistor 46. Conductor
34 also is tapered radially at region 342, its thickness decreasing
at the end nearest transistor 46 as shown in FIG. 2 in order to
reduce the length of its attached conductive spring 40 which
bridges the gap between conductors 34 and 37 and makes spring
contact with the conductor 37. The space between the tapered region
341 and the outer conductor 33 has a tapered ceramic material 43
which is symmetric about the center line 41. The width of the
ceramic material 43 is narrow in the region 44 where the taper 341
of conductor 34 begins, and the width linearly increases in the
axial direction to the end 45 of conductor 34 where the ceramic 43
width is substantially equal to the width of microstrip conductor
37. The combination of the tapered conductor 341 and the inversely
tapered ceramic 43 causes the energy which has been distributed
over the entire region 46 between conductors 33 and 34 to become
concentrated in the ceramic 43 between these same conductors at the
end 45 of conductor 341 while minimizing any impedance
discontinuity. The higher dielectric constant of the ceramic 43
relative to the surrounding air results in the concentration of the
energy within the ceramic. The width of the ceramic 43 in the
region 44 is narrow in order to introduce the ceramic between the
conductors 33 and 34 with a minimum of impedance mismatch.
Typically the width dimension of the ceramic 43 in the region 44 is
only 0.01 inches whereas its width at the other end 45 of the
tapered section 341 is increased to 0.05 inches which is
substantially the width of the mirostrip conductors 37, 38 which
make electrical connection with the input and output terminals,
respectively, of the transistor 46. The base of transistor 46 is
electrically and thermally connected to the ground plane provided
by conductor 33. The emitter and collector of transistor 46 are
connected to the power terminals 18 and 19 to which external
connection is made to power supplies. The transistor mounting base
35 is a thermally conducting ceramic on which the conductors 37 and
38 are formed to provide in combination with the ground plane 33 a
microstrip transmission line. The transistor is typically a
commercially available high frequency FET transistor. A bipolar
transistor is also suitable. The conductors 33 and 34 of the
subassembly 17 are in electrical contact with stepped channel
conductors 24, 26, respectively, by pressure contact provided by
screws 20, 21 in holes 48. The slot 343 in conductor 34 leaves a
portion 344 of conductor 34 which is relatively flexible without
affecting the electrical preparations so that the screw 20 may be
tightened without breaking the subassembly 17.
A stepped cylindrical body 32 fills the space within the stepped
electrical conductor 26 and the region bounded by the subassemblies
17. The cylindrical 32, typically a carbon-loaded epoxy or a lossy
ceramic such as titanate, acts as a microwave absorber which
absorbs any energy which escapes the channels 12 through the slots
28 of conductor 26 or which extend from the transistor subassembly
17. Also, microwave absorbing semi-cylinders 14' and 14", also
typically of the same material as absorber 32, completely surround
the exterior of subassemblies 17 and stepped cylinders 24', 24" and
act as microwave absorbers to energy which escapes or fringes the
slots 13 between the channels 12. The resistivity of the microwave
absorbers 14, 32 may be tapered to prevent lower resistivity in the
immediate vicinity of the slots 13, 28 in order to minimize
reflection of the microwave energy of the undesired modes whose
energy passes through the slots 13, 28. The resistivity may also be
tapered in the direction of axis 27 in accordance with the field
pattern in the axial direction of the undesired mode.
In summary, it is seen that the input energy is first divided into
a plurality of separate channels in a slotted stepped transmission
line 361 into an RF impedance transition region 39 where the RF
energy is concentrated into a small region for introduction on
microstrip lines 37, 38 and out of the transistor 46. The power
output from the individual transistors is combined through similar
microwave lines to be provided at the output connector 16.
The circumferential divider/combiner device 10 is designed to avoid
the reflection difficulties produced by a failed transistor 46 by
effectively isolating one unit from another. The scattering matrix
for the circumferential N-way divider or combiner is: ##EQU1##
where terminal pair 1 is the external terminal and the other N
terminal pairs connect to the individual units. If all terminals
are terminated in matched units, the power splits equally. Any
reflected power resulting from mismatch of a unit does not reach
any other unit directly, but only via reflection of 1/Nth of the
reflected power off the source mismatch. To achieve the zeros in
the scattering matrix, which represent complete decoupling among
the elements, all other modes on the circumferential
divider/combiner circuit except the operating mode, see a match
looking away from the amplifier units. For this purpose, the
isolation elements are tapered. These isolation elements consist of
cylindrical damping resistors at absorbers 14, 32 which are
isolated from the operating mode.
The circumferential divider/combiner device 10 has the geometry
shown in FIG. 4. It has rotational symmetry. When all units are
identical, the voltage on all segments is identical by
symmetry.
A unique difference between the amplifier device of this invention
and prior art is that applicants' device has a means of isolating
the stabilizing damping loads 14, 32 so that device will operate at
higher efficiency than devices constructed using prior art where
dissipative elements were provided by a plurality of isolation
resistors connected between adjacent sectors where parasitic
capacitances caused dissipation in the isolation resistors even in
the operating mode.
Measured data for the ten-channel circumferential divider/combiner
circuit 10 showed that the bandwidth was 70% and the combiner
241/divider 242 loss was 0.2 dB. This means that the more
significant quantity, the equivalent loss for one combiner alone,
is about 0.1 dB. The measurements showed that the inner and outer
external damping resistors did not introduce any loss in the
desired mode. Additional data on the ten-channel circumferential
divider/combiner 10 showed a low VSWR over 11/2 octaves passband
from 4.0 to 12.0 GHZ.
Having described a preferred embodiment of this invention, it will
now be apparent to one of skill in the art that other embodiments
incorporating this invention may be used. It is felt, therefore,
that this invention should not be restricted to the disclosed
embodiment but rather should be limited only by the spirit and
scope of the appended claims.
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